---
title: util
description: Use the Node.js util module in Workers for promisify, callbackify, types, and MIMEType support.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# util

Note

To enable built-in Node.js APIs and polyfills, add the nodejs\_compat compatibility flag to your [Wrangler configuration file](https://developers.cloudflare.com/workers/wrangler/configuration/). This also enables nodejs\_compat\_v2 as long as your compatibility date is 2024-09-23 or later. [Learn more about the Node.js compatibility flag and v2](https://developers.cloudflare.com/workers/configuration/compatibility-flags/#nodejs-compatibility-flag).

## promisify/callbackify

The `promisify` and `callbackify` APIs in Node.js provide a means of bridging between a Promise-based programming model and a callback-based model.

The `promisify` method allows taking a Node.js-style callback function and converting it into a Promise-returning async function:

JavaScript

```
import { promisify } from "node:util";
function foo(args, callback) {  try {    callback(null, 1);  } catch (err) {    // Errors are emitted to the callback via the first argument.    callback(err);  }}
const promisifiedFoo = promisify(foo);await promisifiedFoo(args);
```

Similarly to `promisify`, `callbackify` converts a Promise-returning async function into a Node.js-style callback function:

JavaScript

```
import { callbackify } from 'node:util';
async function foo(args) {  throw new Error('boom');}
const callbackifiedFoo = callbackify(foo);
callbackifiedFoo(args, (err, value) => {  if (err) throw err;});
```

`callbackify` and `promisify` make it easy to handle all of the challenges that come with bridging between callbacks and promises.

Refer to the [Node.js documentation for callbackify ↗](https://nodejs.org/dist/latest-v19.x/docs/api/util.html#utilcallbackifyoriginal) and [Node.js documentation for promisify ↗](https://nodejs.org/dist/latest-v19.x/docs/api/util.html#utilpromisifyoriginal) for more information.

## util.types

The `util.types` API provides a reliable and efficient way of checking that values are instances of various built-in types.

JavaScript

```
import { types } from "node:util";
types.isAnyArrayBuffer(new ArrayBuffer()); // Returns truetypes.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns truetypes.isArrayBufferView(new Int8Array()); // truetypes.isArrayBufferView(Buffer.from("hello world")); // truetypes.isArrayBufferView(new DataView(new ArrayBuffer(16))); // truetypes.isArrayBufferView(new ArrayBuffer()); // falsefunction foo() {  types.isArgumentsObject(arguments); // Returns true}types.isAsyncFunction(function foo() {}); // Returns falsetypes.isAsyncFunction(async function foo() {}); // Returns true// .. and so on
```

Warning

The Workers implementation currently does not provide implementations of the `util.types.isExternal()`, `util.types.isProxy()`, `util.types.isKeyObject()`, or `util.type.isWebAssemblyCompiledModule()` APIs.

For more about `util.types`, refer to the [Node.js documentation for util.types ↗](https://nodejs.org/dist/latest-v19.x/docs/api/util.html#utiltypes).

## util.MIMEType

`util.MIMEType` provides convenience methods that allow you to more easily work with and manipulate [MIME types ↗](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics%5Fof%5FHTTP/MIME%5Ftypes). For example:

JavaScript

```
import { MIMEType } from "node:util";
const myMIME = new MIMEType("text/javascript;key=value");
console.log(myMIME.type);// Prints: text
console.log(myMIME.essence);// Prints: text/javascript
console.log(myMIME.subtype);// Prints: javascript
console.log(String(myMIME));// Prints: application/javascript;key=value
```

For more about `util.MIMEType`, refer to the [Node.js documentation for util.MIMEType ↗](https://nodejs.org/api/util.html#class-utilmimetype).

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